Stan Stokowski

Wafer inspection technology challenges for ULSI manufacturing

The use of wafer inspection systems in managing semiconductor manufacturing yields is described. These systems now detect defects of size as small as 40 nm. Some high-speed systems have achieved 200-mm diameter wafer throughputs of 150 wafers per hour. The particular technologies involved are presented. Extensions of these technologies to meet the requirements of manufacturing integrated circuits with smaller structures on larger wafers are discussed.

Inspecting EUV mask blanks with a 193-nm system

Data and simulation results characterizing the capability of a DUV system to inspect EUV mask blanks and substrates are reported. Phase defects and particles on multilayer (ML) surfaces, ARC-coated absorber, and substrate material are considered. In addition to the previously reported results of inspecting phase defects on multilayer surfaces, phase defects on a quartz substrate surface are shown. The principle of phase detection is described. Simulations show that the 22-nm node requirement for phase defect detection should be met, assuming a reduction in the multilayer roughness. Initial inspections of deposited SiO2 spheres show sensitivities of at least 40 nm on ML and quartz; however, the availability of calibrated spheres of smaller diameters has limited testing below this value. Simulation results show relative sensitivities for detecting SiO2 spheres of different diameters on various EUV materials.

Measuring line-edge roughness of masks with DUV light

Line edges on masks are not perfectly smooth and straight due to writer shot placement errors and randomness in photo-resist processes. This mask roughness may affect local CD defects and CD non-uniformity on the printed wafer. We are able to measure some aspects of line edge roughness using line-space patterns and DUV light in an inspection tool. Analyzing inspection images can make visible both edge placement errors with periodic character (writer generated) and more-random, higher-spatial frequency variations (photo-resist process generated). Our technique observes relative edge placement errors of <1 nm. For example, on one mask the periodic peak-to-peak writer errors are 4 nm, the random edge noise has a standard deviation of about 1.3 nm, and there are ~7 nm steps in the edge position, about one per 200 micron mask field. These values are affected by the inspection tool lateral resolution and thus are actually higher than these values. However, this method is useful in monitoring mask relative edge quality.

Ultraviolet and direct ultraviolet inspection of next generation lithography reticles

The optical inspection of next generation lithography (NGL) patterned reticles, multilayer-coated blanks, and uncoated substrates is particularly challenging. The difficulties arise not only because of the higher sensitivity necessary at the smaller design rules, but also due to the specifics of the NGL mask materials and structures. Our research program is investigating the theoretical and practical operational limitations facing optical inspections of patterned and unpatterned NGL masks. We are constrained by the necessity to inspect only in reflected light, limitations in mask contrast, and interference effects caused by partially coherent illumination. We present inspection results and images of several types of NGL masks, blanks and substrates obtained on high resolution ultraviolet (UV) and direct ultraviolet (DUV) optical mask inspection systems. While electron projection lithography (EPL) stencil masks can be inspected in reflection, limited transmission through the mask suggests that subsurface d...

Optical inspection of next generation lithography masks

For the last 5years a joint venture has pursued a research program studying and enhancing the ability of optical inspection tools to meet the inspection needs of extreme ultraviolet (EUV) and other next generation lithographies (NGLs). In this article we present a survey of results we have obtained for patterned inspection of NGL masks. The NGL technologies that we have studied include two electron projection lithographies, EUV, and step and flash imprint lithography (SFIL). We discuss the sensitivity of the inspection tools and mask design factors that affect tool sensitivity. In contrast to conventional photomask inspection, which primarily utilizes transmitted light for inspection, almost all NGL mask inspections are performed in reflected light. Much of the work has been directed towards EUV mask inspection and how to optimize the mask to facilitate inspection. Early EUV masks had an optical contrast of 40% or lower. Our partners have succeeded in making high contrast EUV masks ranging in contrast fro...

How lasers and optics help increase semiconductor manufacturing yield

Summary form only given. We discuss the requirements of, and solutions for, the inspection problems for the ULSI technology. Preferred embodiments for specific detection problems are described, and the possible limitations, and extensions, of the relevant technologies are discussed.